Bipolar metal-gas batteries can be used for large scale energy storage on spacecraft, and in terrestrial applications such as utility load leveling and electric vehicles. Bipolar batteries of the prior art (see FIG. 1) typically rely on a bipolar plate 11 situated between a positive electrode 7 of one cell 3 and a negative electrode 5 of an adjacent cell 3 in a series-connected battery stack 1. This plate 11 serves two main functions: the electrical connection of the two electrodes 5, 7 and the physical separation of liquid electrolytes present in adjacent cells 3. In battery systems with solid negative and positive electrodes 5, 7, respectively (FIG. 1), this plate 11 can be a simple, relatively thin membrane made of a metal that is stable in the cell 3 environment. When one of the electrodes 5, 7 is a gas electrode (negative electrode 5 in FIG. 2), the function of the plate 11 becomes more complicated, because it must now also provide for gas flow passages to one side of the gas electrode 5 by means of a screen 15. When the positive electrode 7 gasses on overcharge, a porous reservoir 13 may be needed on one side of the solid electrode 7, to temporarily store electrolyte. This further complicates the bipolar structure. In addition, recombination sites for secondary gasses may be needed within or adjacent to the reservoir 13. Thus, the basic structure goes from the simple design of FIG. 1 to the complex arrangement of FIG. 2. A weight penalty is incurred, because the gas flow screen 15 and the reservoir 13 must be metallic to provide electrical conductivity between the negative and positive electrodes 5, 7, respectively. In the present invention, the bipolar plate 11 is eliminated, saving weight; the series electrical connections are made external to the cells 3 themselves. As a consequence, neither the gas flow screens 15 nor the reservoirs 13 have to be metallic. This permits the use of lightweight, nonmetallic compressible screens 15 and reservoirs 13. The compressibility feature is desirable because of gradual expansion of the positive electrodes 7 as they undergo long term electrical cycling.
Koehler, C. W. and vanOmmering, G., "Advanced Bipolar Nickel-Hydrogen Batteries" is a hard copy of a set of viewgraphs that was visually presented but not otherwise disseminated at the U.S. Army Power Sources Symposium in Cherry Hill, N.J., in June, 1984. The sections labeled "Design II" pertain, in a general sense, to the present invention. A subset of these same viewgraphs was visually shown but not otherwise disseminated by the same authors/inventors at the 19th Intersociety Energy Conversion Engineering Conference in San Francisco, California, on Aug. 22, 1984. The vanOmmering/Koehler paper entitled "Bipolar Nickel-Hydrogen Battery System Design" was distributed to the attendees of this conference on Aug. 19, 1984.
Cataldo, R. L. and Smithrick, J. J., "Design of a 35-Kilowatt Bipolar Nickel-Hydrogen Battery for Low-Earth-Orbit Applications", Proceedings of the 17th IECEC, pp. 780-785, dated Aug. 8, 1982; and Cataldo, R. L., "Test Results of a Ten Cell Bipolar Nickel-Hydrogen Battery", Proceedings of the 18th IECEC, pp. 1561-1567, dated August, 1983, disclose nickel-hydrogen bipolar batteries in which metallic bipolar plates and metallic reservoirs are employed.
Adler, E. and Perez, F., "Development of a Large Scale Bipolar NiH.sub.2 Battery", Proceedings of the 18th IECEC, pp. 1568-1573, dated August, 1983, discloses a bipolar nickel-hydrogen battery having heavy metallic bipolar plates that are used for cooling, make short circuits between adjacent cells more likely, and fail to provide for the normal expansion of the positive electrodes.
U.S. Pat. No. 4,098,962 discloses a metal-gas bipolar battery with no bipolar plate, but differing from the present invention in that: (1) no provision is made for confinement of electrolyte or of secondary gas; (2) gas screen 68 must be an electrical conductor; (3) the contacts from screen 68 to the adjacent electrodes are pressure contacts rather than welded contacts; and (4) no electrolyte reservoir is disclosed.
U.S. Pat. No. 4,115,630 discloses a metal-hydrogen battery but not a bipolar battery, as seen from FIG. 2, which shows that connections between oppositely polarized electrodes or adjacent cells skip over intervening non-connected electrodes. The tabs 96,98 shown in FIGS. 5 and 6 are for parallel connections within a single cell, not for series connections between adjacent cells of a multi-cell stack as in the present invention. This patent further differs from the present invention in that: (1) no reservoirs and screens are disclosed; (2) item 34 gives only partial confinement of electrolyte and no confinement of the secondary (oxygen) gas; (3) the teflon coating on the negative electrode is mandatory (column 5, lines 45-52) because hydrogen consumption and oxygen recombination occur here and it is desired to prevent water from flooding the negative electrode, thus blocking gas access. In the present invention, on the other hand, the use of teflon or other hydrophobic coating 39 on the negative electrode 5 is optional since no oxygen recombination is performed there.
U.S. Pat. No. 4,159,367 shows a bipolar metal-gas battery in a gasket frame. The reference battery differs from the present invention in that: (1) it uses bipolar plates; (2) the gas screens must be electrically conductive; (3) the gas screens don't accommodate positive electrode expansion; (4) the gas screens make inferior pressure contacts to the negative electrodes and bipolar plates; (5) no electrolyte reservoirs are disclosed; (6) the gaskets are not stated to be hydrophobic; and (7) secondary gas (oxygen) is confined within each cell but not at sites proximate the positive electrode; as a result, the cells in the reference patent are subject to explosions because the oxygen must travel through the separator to the negative electrode, which is coated with platinum catalyst. Furthermore, no means are disclosed to return the water from the recombination sites on top of the teflon-backed negative electrode back to the positive electrode.
U.S. Pat. No. 4,346,150 discloses a battery in which electrolyte is circulated from cell to cell, rather than confined within each cell as in the present invention.
U.S. Pat. No. 4,420,545 discloses a lightweight metal-gas battery but not a bipolar battery.
U.S. Pat. Nos. 3,846,176, 3,979,224, 4,225,654, 4,317,864, 4,390,602, 4,397,917, 4,414,294, and 4,416,955 pertain to fuel cells, in which the reactants are two gasses or one gas and one liquid, rather than a metal and a gas as in bipolar batteries.